I've gotten it twice now - both times it happened were in areas of really spotty wireless service. First time it happened, restarting the phone in an area with better reception worked, second time I waited about an hour and tried again when I had better service. I use Google to login and it might be because it tried and failed too many times in a short period of time, but that's just speculation. I have an iPhone 6.
Unable to authenticate error
Anyone having issue after recent update? I keep getting "unable to authenticate. Please try again". I can log on fine using my wife's phone. I uninstalled, reinstalled, rebooted after installation, cleared cache and data, issue persists. I was thinking the update rendered my device obsolete, but then why does niantic allow installation. I should get device not supported if that is the case.
Answers
Pokemon app was using google authenticator to contact playstore.google.com, this service was corrupted, that's why rebooting, cleared cache, reinstalled didn't work. Internet connection was not the issue since I was using solid wifi and/or mobile data connections at the time. I was able to play the game until pokemon go force update, so the update must have corrupted some system files. I had no choice but to reset the phone to factory default, and reinstalled everything. Things are now working again.